This project is focused on understanding the basic control mechanisms responsible for expression of the human interleukin 2 (IL-2) gene. IL-2 gene expression is tightly controlled and limited to antigenic stimulation of T cells. In order to study the cell specific regulation of the IL-2 gene we have transfected the human IL-2 gene into mouse NIH-3T3 fibroblasts, human HeLa cells and mouse BFS lymphoma T cells and subsequently analyzed stable transformant cells containing the introduced gene for its expression. All three cell lines were found to express the foreign gene constitutively albeit at low levels. This was evidenced by the presence of both immunoprecipitable protein and bioactivity characteristic of IL-2 in cellular supernatants, as well as mRNA in cellular extracts which hybridized to a human IL-2 cDNA. Curiously, the mRNA species seen was larger than expected for human IL-2 and appears to contain intronic sequences. Treatment with phorbol myristate acetate and the calcium ionophore A23187 resulted in increased expression of the transfected human IL-2 gene in BFS cells but not in 3T3 or HeLa cells. We conclude that the human IL- 2 gene transfected into lymphoid and nonlymphoid cells is constitutively expressed while its protein kinase C/calcium- mediated inducible expression remains restricted to lymphoid cells. Our data are consistent with the occurrence of an imbalance of the interplay of positive and negative regulatory DNA sequences modulating IL-2 gene expression and provide a useful experimental model for their investigation.